The opponent process theory of emotion proposed by Solomon and Corbit (1974) states that there are two processes involved in the regulation of emotion (Figure 1). The first process is the initial reaction to the stimulus, called the α process. For example, if the stimulus (e.g., seeing a bear in the woods) is fear-eliciting, the initial reaction would be that of fear. But, soon after the onset of the α process, a second, homeostatic reaction begins. This is the β process and it opposes the initial reaction to help bring the emotions back into equilibrium. The α process is linked to the presence or absence of the stimulus, but the β process lingers after the stimulus goes away. Therefore, in our example one feels fearful when the bear first appears and feels relief when the bear leaves.

In prior studies we demonstrated that the startled reactions during emotional stimulation track the function predicted by the opponent process theory, but we used a conservative rate of probe stimulation to avoid habituation to the stimulus. This low rate limited our ability to resolve the shape of the opponent process function over time. In addition, the low rate of probe presentation reduced the number of trials over which could average performance. The greater number of trials over which we can average performance will give us more stable means for purpose of statistical analysis. We will consider the pilot study successful if we can double the rate of probe presentation without diminishing the subject's reactivity to the probes.